Mechanisms of demyelination and remyelination are studied in two virus induced demyelinating diseases in (SJL/Balb/c) F1 mice by means of electron microscopy, immunofluorescence and radioautography. The experimental models are murine leucoencephalomyelitis induced by either mouse hepatitis virus (MHV) or DA strain of Theiler's mouse encephalomyelitis virus (DAV). The objectives are to: 1) identify subpopulations of T-lymphocytes in the inflammatory demyelinating lesions at different stages of disease and compare their distribution to lesions produced by allergic encephalomyelitis (EAE). 2) Determine cellular hypersensitivity of spleen cells against mouse spinal cord homogenate (MSCH), myelin basic protein (MBP) and inactivated DAV during the course of DAV induced demyelination. 3) Transfer lymphnode and spleen cells from mice prior to and during the development of white matter lesions after infection with DAV and search for histologic lesions in recipient mice using as positive controls the transfer of lymphoid cells from mice afflicted with EAE. 4) Study remeylination in mice implanted with immunoglobulin producing hybridomas during recovery from MHV infection. The findings are expected to contribute to the understanding of the pathogenesis of human postinfectious encephalomyelitis and multiple sclerosis.